In many industrial processes, the pressure of a fluid flowing in a pipeline must be monitored. For this purpose, a sensor is typically guided into the fluid through the wall of the pipeline. Such apertures through the wall must be sealed against leaks. This makes monitoring pressure labor-intensive.
Therefore, attempts are often made to measure the pressure of the fluid non-invasively, that is to say without direct contact between the sensor and the fluid. Thus, a compact measuring device is known for example from U.S. Pat. No. 7,093,496 A, which device can be applied to an outer periphery of the pipeline by means of a clamp. The clamping force acting between the pipeline and the clamp is measured by a force sensor. This clamping force increases as the pressure in the pipeline rises, since the pipeline expands radially.
EP 88 362 A1 discloses a non-invasive pressure measurement by means of a frequency shift of vibration modes of the pipeline. Vibrations are induced in the pipeline by a variable excitation frequency, and the resonance frequency is determined.
Non-invasive pressure measurements are also further disclosed in FR 2 215 615 A, in WO 1998 037 395 A1, in EP 1 948 924 B1, in EP 210 523 A1, in EP 49 501 B1, in EP 720 006 A1, in DE 10 2009 026 968 A1, in EP 1 657 537 A1 and in DE 10 2009 029 346 A1.
What all the devices and methods disclosed therein have in common is that they react to changes in pressure more or less sensitively, but are not suitable for monitoring absolute pressures in industrial processes because there are too many measurement uncertainties. These uncertainties can be a multiple of 10% of the total measurement range.